Voltage-limiting device



Dec. 27, 1927.

G. T. LORANCE VOLTAGE LIMITING DEVICE Filed Oct. 1925 Patented Dec. 27, 1927.

UNITED STATES PATENT OFFICE.

GEORGE T. LORANCE, OF NEW YORK, N. Y., ASSI IGNOR TO BELL TELEPHONE LABORA- TORIES, INCORPORATED, 01 NEW YORK, N. Y. A-CORPORATION OF NEW YORK.

VOLTAGE-LIMITING DEVICE.

Application filed October '21, 1925. Serial No. 64,049.

This invention relates to signaling systems and more particularly to a method and means for limiting the voltage applied to .a specific part of a transmission system.

In a transmission system, in order to attain a high transmission efiiciency, it is necessary to use various elements included in the circuit at their maximum rated power. In order to do this and to prevent an excess voltage being applied to these elements when the power inthe supply circuit is unexpectedly increased, particularly in the case of high power apparatus where such an overload would cause interruptions of the service, it is desirable to employ a device for limit ing the voltage applied to the power apparatus to a certain predetermined value irrespective of the voltage applied to the input side of the device.

In previously knownsystems, including voltage limiting devices adapted to limit to a predetermined value the voltage supplied to apparatus to be protected, the form of the voltage wave applied to the apparatus may be fiat-topped, that is, of constant amplitude during the time the instantaneous value of the voltage supplied to the limiting device exceeds the desired value. As a fiat-top wave is composed of a component of applied frequency having a maximum amplitude greater than the flat-top, and various harmonics thereof; a Wave of amplitude greater than the predetermined maximum will occur in a circuit which selects the wave of applied frequency and rejects its harmonics.

A system of the above type will only limit the voltage applied to. a load circuit provided this circuit does not discriminate against harmonic frequencies. The, potential across the terminals of any circuit in the system selective to the app ied frequency will not be limited to the predetermined maximum, but will depend upon the length of the flattop portion and the slope of the sides.

An object of this invention is to limit to a predetermined maximum value the voltage of a wave applied to a circuit of the above mentioned character.

Another ob'ect is to limit to'a predetermined value the amplitude of awave of desired frequency in a transmission system, whereby the system may be operated at maximum efliciency.

These objects and others which will be apparent as the nature of the invention is disclosed are accomplished in accordance with the present invention by employing a voltage limiting device comprising two channels, having different transmission characteristics, to which the current to be regulated is applied. One channel includes a space discharge device the amplification characteristicof which may be adjusted with- .in certain limits and the other channel includes a resistance path.

The energy transmitted through the two channels is superimposed in an output circuit in such a manner that as the instantaneous input voltage is increased, the voltage of the output circuit increases up to a certain point and then continuously decreases. Hence, when the input voltage is greater than 'a given value the resultant wave in the output circuit comprises a component of fundamental frequency. and various components harmonically related thereto, but the amplitude of the component of fundamental frequency is always less than the predetermined maximum.

Although the novel features which are believed to. be characteristic of this invention will be pointed out with particularity in -the claims appended hereto, the invention itself, its objects and advantages, the manner of its organization and the mode of its operation will, be better understood by referring to the following description taken in connection with the accompanying drawing forming a part'thereof in which:

Fig. 1 shows diagrammatically one embodiment of this invention, I

gig. 2 illustrates a different form thereof, an

Fig. 3 shows a series of curves to be used in explanation of the operation of the systems shown in Figs. 1 and 2.

Referring to Fig. 1, the input circuit-1 represents the portion of the circuit supplying current to the two transmitting channels which cooperate to-limit to a predetermined v to a load circuit.

value the amplitude of the current supplied Circuit 1 is coupled to the common input circuit of space discharge devices 2 and. 3 by means of a transformer 4. Space discharge devices 2 and 3 are connected in opposing. or so-called pushpull relationship in such a manner that currents in the output circuit of one tube increase as current in the output circuit of the other tube decreases; The output circuits of tubes 2 and 3' are coupled by means of a transformer 6 to the filter F. This filter is adapted to pass, without appreciable attenuation, current of a definite frequency or a band of frequencies below a certain cut-off frequency to transmission line 8.

Resistance 9 and condenser 11 are connected between the grid and anode of tube 2 and resistance 10 and condenser 12 are connected between the grid and anode of tube 3 to form a shunt path between the input and output circuits of the device for the purpose to be hereinafter set forth. The condensers 11 and 12 are of large capacity, so that their impedance to the energy transmitted through the channels is negligible. In other words, the impedances of the shunt paths are determined by the resistances 9 and 10.

The operation of this system may be best understood by referring to the series of curves in Fig. 3. In that figure curve (1 represents the amplification characteristic of the channel including space discharge devices 2 and 3, the voltage in the input circuit being plotted against the voltage of the anode circuit. Curve 6 represents the transmission characteristic of the resistance paths between the input and anode circuits through resistances 9 and 10. Inasmuch as phase reversal occurs in space discharge devices 2 and 3, whereas currents in the shunt circuits including resistances 9 and 10 are transmitted without phase change, the corresponding Voltages produced in response to the voltage impressed from line 1 will be in opposed relationship in the anode circuit of the space discharge channel. Hence the resultant current may be found by subtracting the ordinates of curve I) from those of curve a. The result isplotted as curve 0. The peak value of this curve may be controlled by varying the amplification characteristic of the amplifying channel or by varying the transmission characteristic of the parallel resistance channel to produce transmission characteristics represented by curves a and b.

It will be seen in curve 0 that as the voltage E applied to the input'circuit is varied between the limits zero and E the voltage E at the output terminal will be directly proportional to voltage E but as the input voltage E increases beyond the value E the voltage of the output circuit E decreases. It is apparent therefore that, irrespective of the maximum value of voltage E the maximum instantaneous value of the voltage E may be limited by adjusting the channels to produce the desired transmission characteristics such,.as shown in curves at and 6 whereby the apparatus connected to the circuit 8 may be protected against instantaneous voltages greater than the limiting value.

If an alternating voltage having a maximum peak voltage less than E is applied to line 1, a voltage having the same wave form will occur in line 8. If the peak voltage of the applied wave is greater than E the voltage applied to the filter will no longer be of the same form as the applied ware. Instead of a flat-top wave, such as that produced by previously known voltage limiting systems, a wave having a dip in its top portion will be supplied to the filter F due to the decrease'in the value of voltage in E as voltage E is increased beyond 15,. Thus there will be supplied to the filter a wave consisting of a component of frequency corresponding to the impressed wave the maximum amplitude of which is limited to a predetermined value and components harmonically related thereto.

The amplitude of the harmonics depends upon the amount by which the maximum potential E exceeds voltage E and the constants of the transmission channels. Hence, if the constants are properly selected, as the amplitude of voltage E is increased to a certain value, thegfvoltage of the fundamental frequency in the output circuit becomes a maximum and then decreases, but as the voltage E is further increased only the harmonics are increased in amplitude. Since the filter F suppresses the harmonics, while it passes the fundamental frequency substantially without attenuation there will be supplied to the line 8, or apparatus connected thereto, a voltage wave. corresponding to the impressed wave, the maximum value of which is fixed and indepcmlent of the voltage applied to the limiting device over line 1.

By suitably selecting the values of rollages E and E the third harmonic may be made predominant. It means selective of the third harmonic is included in line 8, this arrangement may be used to produce a wave of frequency, triple that of the. wave received over the line 1.

Referring to Fig. 2, current from line 1 is transferred by means of transformer 20 to the input circuit of amplifier tube 21. The output circuit of amplifier .21 is coupled to the input circuit of space discharge device 22 by means of condenser 23 and inductance 24. Battery 27 is adapted to impress a negative biasing potential upon the control electrode or rid of tube 22. The circuit through whicfi biasing potential is suppl ed to the grid includes a resistance 25. Resistance 2.8 and condenser 29 form a shunt path between the input and output circultsot tube 22. As described in connection-with Fig. 1, the impedance of the shunt path is determined'by resistance 28. Current in the output circuit of this tube is transferred by means of transformer 30 to filter F which is adapted to pass currents of a given frequency, or a band of frequencies, to transmission line 31. V

In certain cases, it may be desirable to use a resistance 26 in series with the primary of the transformer 30. This resistance appears to operate to establish a definite ratio between the impedance of the circuit external to the tube as the cathode-plate impedance of the tube, whereby the current transmitted through the shunt path 2829 may be in the desired phase relation, with respect to the wave impressed upon the input circuit, to properly control the operation of the tube as a limiting device. Obviously, if the impedance of the output circuit, including the transformer. 30, is of the proper value to produce the desired ratio, the resistance, 26 Will not be used.

Amplifier tube 21 serves to raise the potential of the applied wave to a value sufliciently large to operate the voltage limiting apparatus and to compensate for the loss inherent therein. An additional function is served by tube 21, however, in that when the input voltage has increased to a' value sufiicient to cause curve a to pass the zero axis, beyond which point the absolute value of the output voltage would again increase, amplifier 21 will reach its overload oint and preventfurther increase in potentlal.

Consequently, the system as a whole including amplifier 21 will positively prevent the output voltage from exceeding the peak value represented by curve a irrespective of the applied voltage. Obviously, such an amplifier may be incorporated in the circuit arrangement shown in Fig. 1 to produce the same result.

The operation of the circuit shown in Fig. 2 including space discharge path 22 and shunt resistance path 28 is similar to that of Fig. 1 and may be understood by reference to the description of the operation of Fig. 1 and the curves illustrated in Fig. 3.

Although this invention has been shown and described as applicable to a particular system, it is not to be limited thereto, but only in accordance with the scope of the following claims.

What is claimed is:

1. In a signaling system an incoming line and an outgoing line, a voltage limiting device comprising a pair of transmission channels connected between said lines transmitting waves in phase opposition to said outgoing line, one of said channels including a space dischar e amplifier.

2. In a signa ing system an incoming line and an outgoing line, a voltage limiting device comprising a pair of transmission channels connected inv phase opposition, one of said channels including a. space discharge amplifier and the other of sald channels including aresistance path.

v3. A voltage limit-ing device, comprising a pair of transmission channels, one of said channels including a space discharge amplifier and means for governing the transmission characteristics of said amplifier, the other of said channels including a resistance path, and a space discharge amplifier connected between the input circuit and said channels whereby the value of the current impressed upon said channels is controlled.

4. In a signaling system, an'incoming line and an outgoing line, two transmission channels therebetween, common input means in said channels, one of said channels amplifying waves from said incoming line, the other of said channels transmitting said waves with substantially no amplification, cormon output means to impress the difi'erence in amplitudes of the outputs of said channels on said outgoing line to limit the voltage in said outgoing line irrespective of the voltage in said incoming line.

5. In a signaling system, an incoming line and an outgoing line, two transmission channels therebetween, common input means for said channels, one of said channels comprising a space discharge amplifier for amplifying the waves from said incoming line, the other of said channels transmitting said waves with substantially no amplification, output means common to said channels for impressing the outputs of said channels on said outgoing line in opposite phase relation to limit the voltage in said outgoing line.

6. In a signaling system, an incoming line and an outgoing line, two transmission channels therebetween, input means common to both channels, one of said channels comprising a space discharge amplifier for amplifying waves from said incoming line, the other of said channels comprising substantially a resistance path and transmitting said waves with no amplification, output means common to said channels for impressing the outputs of said channels on said outgoing line in opposite phase relation to limit the voltage in said outgoing line to a predetermined value. I

7. In combination in a signaling system. an incoming line and an outgoing line, a voltage limiting device comprising a plurality of transmission channels between said lines, input means common to said channels, one of said channels comprising a space discharge amplifier for amplifying and reversing the frequencies in said incoming line, the other of said channels comprising a substantially pure resistance path for transmitting the frequencies from said incoming 5 line with no phase change, output means common to said channels for impressing the difi'erence in amplitude of the outputs of said channels on said outgoing line for con- =anda filter in sai trolling the Volta e in said outgoing line,

output circuit for atten- 1 uating certain of said incoming frequencies. 1

In Witness whereof, I hereunto subscribe my name this 20th day of October, A. D., 1925.v

GEORGE T. LORANOE. 

